Class 12 Physics First law of thermodynamics Notes and Important Questions
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Notes for Class 12 First law of thermodynamics (Physics) are shown above.
Practice
Important Questions
A system undergoes an isochoric process so that its temperature changes from 127°C to 227°C. What is the ratio of initial pressure to final pressure?
4/5
5/4
227/127
127/227
An ideal gas is taken through series of changes represented in the diagram below. The net work done by the gas at the end of the cycle is equal to
P₁V₁
12P₁V₁
6P₁V₁
3P₁V₁
What happens in an adiabatic process?
Volume remains constant
Pressure remains constant
Temperature remains constant
The system is insulated from the surroundings
Draw a PV diagram of a petrol engine and explain its working based on its PV diagram.
Compare the efficiency of petrol engine with that of diesel engine based on their compression ratios.
An ideal gas is taken through series of changes represented in the diagram below. The net work done by the gas at the end of the cycle is equal to
P₁V₁
12 P₁V₁
6 P₁V₁
3 P₁V₁
What is the coefficient of performance of an ideal refrigerator working between ice point and room temperature ?
$0$
$1$
$10$
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Exam
Past Question Analysis
Historical exam-pattern data from past NEB question papers — not a prediction of future questions.
10
Question Items
6
Total Marks
5
Papers Appeared In
| Year | Question Items | Marks |
|---|---|---|
| 2083 | 2 | 1 |
| 2082 | 2 | 1 |
| 2081 | 1 | 1 |
| 2080 | 3 | 1 |
| 2078 | 2 | 2 |
Also appears in 7 model questions (not counted above — model sets aren't actual NEB exam history).
The First Law of Thermodynamics explains the relationship between heat, work and internal energy. Students explore different thermodynamic processes, heat capacities, and the behavior of gases during isothermal and adiabatic changes.
This page covers First law of thermodynamics, chapter 4 of 25 in the Class 12 Physics syllabus set by the National Examination Board (NEB). 15 important questions for this chapter are available, each with a full solution.
For numerical and derivation-based chapters like this one, working through past NEB questions is usually more useful than re-reading notes alone — try solving each important question above before checking the solution, then compare your working step by step.